A hydraulic control valve in the related art, as shown in FIGS. 1 to 3, includes a valve block B in which an inlet port P1 and an outlet port P2 that communicates with the inlet port P1 are formed; a first check valve C1 installed to open and close an intersection portion of a path 1 (1) communicating with the inlet port P1 and a path 4 (4) communicating with the outlet port P2, the first check valve C1 permitting a flow of hydraulic fluid from the path 1 (1) to the path 4 (4) and limiting a flow of the hydraulic fluid from the path 4 (4) to the path 1 (1); a second check valve C2 installed to open and close an intersection portion of a path 3 (3) communicating with the path 4 (4) and a path 2 (2) communicating with the path 1 (1), the second check valve C2 permitting a flow of the hydraulic fluid from the path 2 (2) to the path 3 (3) and limiting a flow of the hydraulic fluid from the path 3 (3) to the path 2 (2); and a spool S slidingly coupled to the valve block B to control the flow of the hydraulic fluid from the outlet port P2 to the inlet port P1 through the second check valve C2 that is opened when the spool S is shifted by pilot signal pressure Pi.
In the drawings, the reference numeral R denotes a relief valve that protects a hydraulic circuit by feeding the hydraulic fluid that corresponds to excessive pressure back to a hydraulic tank T when pressure that exceeds a predetermined pressure is generated in the path 4 (4).
According to the hydraulic control valve in the related art, the hydraulic fluid that is supplied to the inlet port P1 flows to the outlet port P2 through the path 1 (1), the first check valve C1, and the path 4 (4) in order.
At this time, since the first check valve C1 is maintained in a closed state by the pressure in the back pressure chamber 5 of the first check valve C1 and the elastic force of a spring 10, the hydraulic fluid does not flow from the path 3 (3) to the path 2 (2).
On the other hand, if the spool S is shifted upward as shown in FIG. 1 according to the supply of the pilot signal pressure Pi (in FIG. 3, the spool S is shifted to the right side by the pilot signal pressure Pi), a path b (8) communicates with a path c (9) formed on the spool S, and thus the pressure in the back pressure chamber 6 of the second check valve C2 becomes equal to the pressure of the inlet port P1.
At this time, since the pressure of the path 3 (3) becomes higher than the pressure of the back pressure chamber 6, the second check valve C2 is shifted to the right side as shown in FIG. 1 (in FIG. 3, the second check valve C2 is shifted upward by the pressure of the path 3 (3)). Through this, the path 2 (2) that communicates with the path 3 (3) communicates with the path 1 (1) through the spool S shifted upward.
Accordingly, the hydraulic fluid in the outlet port P2 is supplied to the path 1 (1) that communicates with the inlet port P1 through the path 4 (4), the path 3 (3), the path 2 (2), and the spool S in order.
As described above, in the case of controlling the flow of the hydraulic fluid from the outlet port P2 to the inlet port P1 of the hydraulic control valve by the pilot signal pressure Pi, a large-size spool S that is shifted by the pilot signal pressure Pi is required so that the pressure of the back pressure chamber 6 of the second check valve C2 can be controlled and the hydraulic fluid can flow from the inlet port P1 to the outlet port P2 with a small loss of pressure.
Due to this, since the hydraulic control valve that is coupled to the large-size spool is large-sized, the manufacturing cost is increased to weaken the competitive power, and the work to mount the large-sized control valve on the hydraulic cylinder becomes difficult to cause inconvenience in manufacturing the hydraulic control valve.